The present invention relates to a V-belt drive unit comprising asymmetric or nonsymmetric V-belt pulleys. Each pulley has side walls hereinafter referred to as belt contacting flanks or pulley flanks or simply as flanks. One flank of a pulley extends approximately radially relative to the rotational axis of the pulley. The other flank extends at a larger angle relative to said rotational axis. Further, the sloping angles of these pulley flanks relative to the radial direction are smaller by at least one degree than the corresponding sloping angles of the V-belt flanks.
German Patent (DE-PS) No. 2,001,623 discloses a V-belt drive unit of the just described type. In the prior art nonsymmetric or asymmetric V-belt drive units the input pulleys and the output pulleys are of the same construction relative to each other. Stated differently the flanks in the prior art drive unit have the same sloping angle on one side of the input and output pulley and also the same sloping angle on the other side of the input and output pulley.
The prior art V-belt drive unit is constructed for smaller transmission ratios. Stated differently, the prior art unit is quite suitable for the transmission of a given power up to a certain pulley diameter. However, there is a need for asymmetric or nonsymmetric V-belt drive units having larger power ratings for the transmission of respectively larger powers. For this purpose it is necessary to increase the pulley diameter. Prior art V-belt drive units as mentioned above are not suitable for such larger power ratings or are not adapted for the transmission of such larger powers. It has been found that by increasing the running diameter in a prior art V-belt drive unit the asymmetric V-belt itself is subject to a twisting, whereby the power transmission is limited.